1. Field of Disclosure
This invention relates in general to wellhead assemblies, and in particular to energizing rings used to lock down concentric tubular members.
2. Description of Related Art
Wellhead assemblies can include concentric tubular shaped members. Outer and inner wellhead members can be, for example, a wellhead housing, casing hanger, tubing hanger, seal assembly, or other member with a generally ring shaped cross section. Throughout the life of the wellhead assembly, forces within the wellhead assembly can push the inner wellhead member axially up and down. As an example, when the wellhead members are subjected to high pressures, the high pressures can cause the inner wellhead member to move axially upward relative to the outer wellhead member. Thermal expansion can also lead to relative axial movement between outer and inner wellhead members.
Small relative axial movement can also occur between the inner wellhead member and the outer wellhead member due to stack up tolerances. This motion can cause wear of the adjacent surfaces, jeopardizing the integrity of the inner wellhead member and the outer wellhead member. Relative movement between components is, for example, of particular concern for metal to metal seal elements. In cases where small relative axial movement is undesirable, a preload force can be generated through the load path between lockdown ring flanks and mating faces of an annular recess within the entire stack up tolerance range, to reduce or eliminate any relative axial movement between the inner wellhead member and the outer wellhead member.
A lockdown ring can be used to prevent or reduce relative axial movement between outer and inner wellhead members. Lockdown rings can be energized by an energizing ring. Once the energizing ring energizes the lockdown ring, the energizing ring stays in place to maintain the radial position of the lockdown ring. In some current wellhead systems, continued pressure and force from the lockdown ring on the energizing ring, can be sufficient to move the lockdown ring from the set position to an unset position. In addition, due to the stack up tolerances, the lock ring may not land in a predicable location and may not provide sufficient locking forces to prevent relative movement between outer and inner wellhead members.
In some current energizing rings, the engaging surfaces of the energizing ring are straight. Such energizing rings can only displace the lock ring a set radial amount. Therefore depending on the stack up tolerances, such energizing rings can allow for more than acceptable amounts of relative axial movement between the inner wellhead member and the outer wellhead member.
In other current energizing rings, a taper can be incorporated into the energizing ring. A tapered energizing ring interface ensures contact of the lock ring flanks throughout the stack up tolerance range but requires an additional lock down device for the energizing ring, which can require a separate tool and additional trips into the well to operate. In addition there is not positive stop for the energizing ring so the exact set position of the energizing ring will be unknown.